Electric discharge lamp



Oct. 10, 1939. A. G. STIMSON ELECTRIC DISCHARGE LAIP Filed June 16, 1938 INSULA T MIG NA TEE/AL Inventor:

Allen 6. Stims n,

ttorne g.

Patented Oct. 10,- 1939 UNITED STATES ELECTRIC DISCHARGE LAMP Allen G. Stimson, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application June 16, 1938, Serial No. 214,012

' 11 Claims.

My invention relates to electric discharge lamps and particularly to starting apparatus therefor. The object of my invention is the provision of improved apparatus of this character which is simple in construction, emcient and economical in operation and inexpensive to manufacture.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the single figure of the drawing, I have represented at I an electric discharge lamp such for example as a sodium vapor lamp having at the ends thereof the anodes 2 and 2" and the filamentary cathodes 3 and 4, each cathode being connected at one end with the adjacent anode and at the other end with one of the lamp terminals by which energy is supplied to the lamp. The source of energy supply is represented at 5 as being an alternating current circuit of the constant current type such as is commonly used in series lighting systems. Energy is shown taken from the circuit 5 by means of the series transformer 6 between the ends of the secondary of which and the lamp I'have shown the usual film cut-out I, the radio frequency capacitor 8 and the radio frequency choke .9.

In order that the lamp cathodes may be heated to the desired temperature and suitably activated before the discharge starts in the lamp I connect them at starting by a low resistance circuit for a predetermined time after which the circuit is automatically opened and the discharge starts. For this purpose I have provided a switch and a time delay apparatus for operating it comprising the bimetallic device III which is heated by the current traversing it and which comprises a number of series connected loops secured to the fixed insulating bar II at one end and to the movable insulating bar I2 at the other end. The central tongue l3 of the device secured to the bar l2 carries the screw H whose function will be presently described. By means of this construction compensation is effected for variations in the temperature of the ambient.

Arranged behind the device I0 is the switch comprising the fixed contact l8 and the co-operating movable spring contact I! mounted on the end of the armature l8 which is pivoted at l9 and is biased by the spring 20 to a position at which the switch contacts are in closed circuit position. The bimetallic device and the switch are connected in a series circuit between the lamp cathodes and hence also between the lamp anodes whereby the current traversing the switch and to a predetermined degree by the current passing 6 through it, however, it is warped so that the screw H engages the armature I8, pushing it against the spring 20 thereby reducing the air gap between it and the core 23 until finally the spring contact ll disengages the contact It, thus opening the heating circuit of the device. The cathodes must not only be heated to the proper degree but the heating thereof must continue for a definite length of time, particularly in the case of sodium lamps in order that the cathodes may be activated before the discharge starts. The device is so constructed that the time which elapses before it thus opens the circuit is sufficient for the cathodes to become heated to the desired temperature and to become activated. By reason of the construction of bimetallic device which I have provided the desired length of the time delay, which may be from 25 to 45 seconds, is provided while there is also obtained sufiicient movement and power in the tongue l3 with the current available "to actuate the switch with certainty under the varying conditions found in service.

When the switch I6, I! is opened by the bimetallic device ID the discharge starts in the lamp; The switch thereafter is held open by the electromagnet 22 which is connected across the anodes to shunt the discharge in the lamp and which is constructed to offer a high impedance to the alternating current but to have a low ohmic resistance. By reason of the latter it will be better able to withstand excess voltage in the event of an open circuit failure of the lamp and a failure of the cut-out l to function when it is subjected to the full open circuit voltage of the transformer 8. The magnet has a laminated core 23 which carries the winding 24, the magnetic circuit being completed by a yoke comprising the part 25 and the armature 18,. The free end of the core has the shading winding 26 whereby the fiux between the core and the armature may be more uniform and the armature less liableto be released between the half cycles of the main flux. At the junction of the core and the part 25, I have provided the non-magnetic plate 21 for insuring a fixed gap in the magnetic circuit better to insure the release of the armature when the main circuit is no longer energized. when so released,

the contacts l6, I! are again closed, the screw l4 that voltage on the opposing ha. cycle of voltage of the alternating current, for although the direct current voltage is small in comparison with the alternating current voltage the direct current component may be approximately equal to the alternating component by reason of the low resistance of the winding. This trouble may be overcome by increasing the moment of inertia of the armature but I prefer to overcome it by the use of a capacitor shown at 28 in series with the winding 24 thus blocking the passage of direct current to the winding. The capacitor and the winding are so proportioned that they fornra resonant circuit at the voltage normally existing between the anodes of the lamp when it is operating, which for example may be 19 to 25 volts.

,Hence the winding is made with a materially higher impedance than if the capacitor were not used. Should a failure occur in the lamp whereby a discharge does not start therein or the discharge stops after it has started and the capacitor and winding be thereby subjected to the full voltage produced by the transformer 8 which may, for example, be about 85 volts, the core 23 saturates and the condition of resonance no longer exists. The winding 24 is able to withstand this higher voltage without overheating and the power loss in the winding after saturation occurs is much less than it would be were the capacitor not used. The combined impedance of the winding and the capacitor is high enough to cause the film cut-out 1 to function in the event of such a failure of the lamp.

I have chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various modifications may be made without departing from the spirit and scope of my invention which modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. Starting apparatus for an electric discharge lamp having therein an anode and a co-operating cathode arranged to be connected with opposite sides of a source of current supply comprising means for completing a circuit between said anode and cathode whereby the cathode is heated by the current in the circuit, time delay means for opening said circuit and means responsive to the voltage between said anode and cathode for holding said circuit open.

2. Starting apparatus for an electric discharge lamp having therein an anode and a co-operating cathode arranged to be connected with opposite sides of a source of current supply comprising means for completing a circuit between said anode and cathode whereby the cathode is heated by the current in the circuit, time delay means responsive to the current in said circuit for opening the circuit and means responsive to the voltage between said anode and cathode for maintaining said circuit open.

3. Starting apparatus for an electric discharge lamp having therein spaced anodes arranged to be connected with opposite sides of a source of supply ofalternating current and filamentary cathodes each arranged adjacent to and connected with one of said anodes comprising a switch, heat respon sive means for opening said switch, means conmeeting said switch and said device in a series circuit between said anodes and means responsive to the voltage between said anodes when said switch is opened for maintaining it in open position. e

4. Starting apparatus for an electric discharge lamp having therein spaced anodes arranged to be connected with opposite sides of a source of supply of alternating current and filamentary cathodes each arranged adjacent to and connected with one of said anodes comprising a switch, heat responsive means for opening said switch, said switch and said means being arranged in a series circuit connected with said cathodes whereby the cathodes are heated by the current passing the switch and the means, and a device responsive to the voltage across said anodes for holding the switch in open position.

5. Starting apparatus for an electric discharge lamp having therein spaced anodes arranged to be connected with opposite sides of a source of supply of alternating current and filamentary cathodes each arranged adjacent to and connected with one of said anodes comprising a switch biased to closed circuit position, a bimetallic device for opening said switch, means connecting said switch and device in series between said anodes and an electromagnet connected between said anodes for maintaining the switch in open position in response to a predetermined arc voltage drop.

6. Starting apparatus for an electric discharge lamp having therein spaced anodes arranged to be connected with opposite sides of an alternating constant current circuit and filamentary cathodes each arranged adjacent to and connected in series with one of said anodes comprising a switch biased to closed circuit position, a bimetallic compensating member heated by the current flow therethrough for moving said switch to its open circuit position when heated, means connecting said switch and said member in a series circuit between said anodes and an electromagnet responsive to a predetermined voltage between said anodes for holding said switch in the open circuit position.

'7. In combination, an electric discharge lamp having therein spaced anodes and thermionic cathodes arranged to be supplied by a source of current, a switch biased to closed circuit position, a device responsive to the voltage between said anodes for holding said switch in open circuit position and a time delay device connected between said anodes and in series with said switch for moving the switch to open circuit position.

8. In combination, an electric discharge lamp having therein spaced anodes and thermionic cathodes connected therewith arranged to be supplied by a source of current, a switch biased to closed circuit position, a high impedance electromagnet connected between said anodes, said magnet having an armature secured to one contact of said switch and a bimetallic device connected in series with said switch between said anodes for moving said armature and contact to open circuit position, said armature and switch being held in open circuit position by said magnet.

9. In combination, an electric discharge lamp having spaced electrodes therein arranged to be supplied by a source of constant current, voltage responsive short-circuiting means between said electrodes, starting means for said lamp, electromagnetic means connected between said electrodes and responsive to the arc voltage drop of said lamp for holding said starting means inoperative, the impedance of said electromagnetic means being sumciently high to cause said voltage responsive short-circuiting means to function if an open circuit failure occurs in the lamp.

10. In combination, an electric discharge lamp having therein spaced anodes and thermionic cathodes arranged to be supplied by a source of current, means for causing an initial heating of said cathodes, an electro-magnetic device responsive to the arc voltage drop of said lamp for holding said means inoperative and a capacitor in circuit with said device, said capacitor and device being in resonance at the normal operating arc voltage drop of the lamp.

11. Starting apparatus for an electric discharge lamp having therein an anode and a cooperating cathode arranged to be connected with opposite sides of a source of current supply comprising means for completing a circuit between said anode and cathode whereby the cathode is heated by the current in the circuit, time delay means for opening said circuit whereby an arc is produced between the anode and cathode, and means responsive to the voltage across said arc for holding said circuit open.

ALLEN G. STIMSON. 

